Habitat features mediate selective consumption of salmon by bears

Abstract

Salmon provide a key source of marine-derived nutrients to aquatic and surrounding terrestrial habitats in coastal areas of the North Pacific. Bears are a major predator of salmon and provide an important pathway for carcass transfer to riparian zones. We studied selective consumption of salmon (Oncorhynchus keta and Oncorhynchus gorbuscha) by bears (Ursus arctos and Ursus americanus) on 12 streams on the central coast of British Columbia, Canada. We predicted that bears would select more energy-rich parts, and eat less of each fish (i.e., selective consumption), in streams with more prey and simpler habitat (i.e., streams that facilitate salmon capture). Bears were 12% more likely to consume fish selectively in narrow, shallow streams with less pool volume, where salmon are easier to catch, than in deep, wide streams. However, bears were also 21% more likely to selectively consume fish in streams with more wood obstacles and undercut banks, where hunting was predicted to be more difficult. This suggests that stream characteristics can have significant indirect effects on riparian nutrient subsidies to ecosystems through selective feeding by bears.